Prostate cancer is the most prevalent non-cutaneous malignancy in American men, with estimates for 2007 at over 218,000 new cases and 27,000 deaths. The developmental transcription factors SOX4 and HOXC6 are strongly correlated with prostate cancer progression. During the past three years, we have identified hundreds of direct targets of these transcription factors, elucidating the transcriptional networks that they regulate, and providing mechanisms for their action. Insights from our studies suggest that SOX4 and HOXC6 represent novel links between the Wnt and Notch pathways. Both the Wnt and Notch pathways are conserved developmental pathways that are often activated in human cancers and that represent new opportunities for therapeutic intervention. SOX4 is both a target and effector of the Wnt pathway and directly interacts with ?-catenin to activate gene expression. Our preliminary studies show that HOXC6 normally provides negative feedback to the Wnt pathway, but this feedback is lost during oncogenesis via epigenetic silencing of HOXC6 target genes. We have also discovered that SOX4 and HOXC6 regulate several Notch pathway components and Notch downstream targets. Thus, we hypothesize that overexpression of SOX4 and HOXC6 results in cooperative activation of the Wnt and Notch pathways during prostate cancer progression and metastasis, maintaining an undifferentiated, transit-amplifying, progenitor cell phenotype. SOX4 and HOXC6 also activate expression of several growth factor receptors that promote cancer cell growth and survival. Furthermore, we have new data suggesting that SOX4 and HOXC6 work in concert to alter miRNA and protein-coding gene expression to promote cell survival in the presence of genomic instability and DNA damage. In light of our continued progress and new exciting preliminary data, we plan to increase our understanding of how these key oncogenic transcription factors contribute to cancer progression and metastasis through three specific aims. We will test whether HOXC6 and SOX4 cooperate to activate Notch signaling in vitro and in animal models with prostate-specific, inducible expression of these genes. We will test whether SOX4 is a crucial link between the Wnt and Notch pathways, and whether HOXC6 can repress Wnt signaling upon treatment of cells with demethylating agents. Finally, we will test whether SOX4 and HOXC6 regulate predictive biomarker genes involved in cellular responses to genomic instability. These proposed studies will provide fundamental knowledge highly pertinent to many types of cancer, new mechanistic insights specifically into prostate cancer bone metastases, and preclinical data that could lead to new clinical trials for treatment of metastatic prostate cancer patients with poor prognoses.